A lithium ion secondary battery (hereinbelow, a lithium ion battery) utilizing absorption and desorption of lithium ions for charge-discharge reactions attracts great expectations as a battery that can be used in various applications such as a power supply for a portable electronic device such as a mobile phone and a notebook computer, an auxiliary power supply for disasters, and a power supply for a moving vehicle such as a car and a motorcycle for the reasons that larger energy density than that of a conventional lead battery or nickel-cadmium battery can be obtained, that lithium contributing to the charge-discharge reactions is rarely deposited on electrodes as metal lithium, that reproducibility of the capacity after repeated charge and discharge is excellent to provide a stable charge-discharge characteristic, and the like.
In particular, examples of the car are a zero-emission electric car mounting a motor driven by power from the secondary battery and traveling by means of the driving force from the motor, a hybrid electric car mounting both an engine using fossil fuel and the motor, and a plug-in hybrid electric car charging the secondary battery directly from a system power supply.
In a case in which this lithium ion battery is mounted on the hybrid car, the zero-emission electric car, or the like, the lithium ion battery often employs a structure in which a plurality of battery cells are connected in series, in parallel, or by combining the serial connection with the parallel connection to constitute an assembled battery (a battery module), and in which the battery module is housed in a chassis since load voltage and load capacity required for the lithium ion battery increase.
In each battery cell of the lithium ion battery, the electrodes expand at the time of charge and discharge, and a distance between a positive-electrode terminal and a negative-electrode terminal is enlarged, which causes an increase in internal resistance and reduction in output. Thus, the expansion needs to be restricted. Also, the battery cell is constituted by a metallic exterior can, and when the exterior cans having different potentials are electrically connected, short circuit current flows. Thus, the battery cells need to be insulated from each other.
For these reasons, there is proposed a battery block in which a plurality of rectangular battery cells each having a positive-electrode terminal and a negative-electrode terminal on an equal surface are arranged and laminated, having a structure in which spacers directly holding the battery cells and keeping the insulating state between the adjacent battery cells and a pair of highly rigid end plates at both ends of the battery block are arranged in a laminating direction of the battery cells, and in which a distance of the endplates is kept constant in a state in which the endplates are pressed from both the ends by a coupling and fixing tool (refer to PTL 1).